ELK-BLT Battery LifeTester
Application
The ELK-BLT Battery Life Tester or “Mhos Meter” is a
compact, easy to use service tool for testing 12 Volt
rechargeable batteries. The BLT measures internal
conductivity (Mhos), which is the best indicator of a
battery’s health and life expectancy. Mhos happens to
be the inverse of Ohms (conductance as opposed to
resistance). The BLT operates as follows: For each
battery brand and size installed you should start by
measuring and recording a “baseline” Mhos reading.
Then, during any service call or inspection simply
measure and record the current (most recent) Mhos
reading. Always compare the current Mhos reading with
the original reading. Self-adhesive test data labels may
be used for recording each inspection. When the
current Mhos reading has reached at or around 71% of
the original baseline then it is time to consider changing
the battery. The BLT includes a reference chart on the
back with numbers equating to Mhos readings for
common security industry battery sizes.
a.k.a Battery Mhos Meter ver 3.0
The BLT receives its operating power from the battery
under test and automatically warns when the battery
voltage is too low for testing.
Features
• Does not discharge or damage the battery.
• Tests 12 Volt Rechargeable Batteries.
• Display Shows Battery Voltage and Mhos.
• Warns if battery voltage is too low.
• Replaceable test leads.
• Includes padded carrying case.
• Includes self-adhesive test data labels. **
• Lifetime Limited Warranty.
Specifications
• Operating Voltage: 10.0V - 14 Volts D.C.
• Current Draw: 1.1 Amps Max., 0.0016 Ah for full test.
• Battery Leads: ~12 Inches.
• Size: 4.4” W x 3”H x 1.15”D w/o carrying case.
** To reorder a pack of 100 test data labels specify: ELK-BLT LABELS.
PO Box 100 • Hildebran, NC 28637 • 800-797-9355 • 828-397-4200
Fax 828-397-4415 • www.elkproducts.com • info@elkproducts.com
03/1/08
ELK
PRODUCTS, INC.
Instructions
BLT measurements should be taken and recorded periodically. The popular method is to record the information onto self-adhesive
labels placed directly onto the battery. A supply of these labels is included with the tester. Additional labels may be ordered in
packs of 100 by specifying part number ELK-BLT LABELS. This information will be valuable in future tests for trending analysis.
The recorded data should include:
A. The Date of the test.
B. The Battery Voltage reading. (optional)
C. The Mhos reading.
1. Disconnect the battery from it’s equipment.
2. Connect the BLACK test clip to the Negative (-) battery terminal, and the RED to the Positive (+) terminal. (For accurate
readings, the test clips must be tightly clipped directly to the battery posts, not to the battery bolts).
“Err” or blank indicates battery voltage is too low for testing or a test clip connection is loose.
Try charging the battery or reconnecting the test clips.
3. The Voltage of the Battery will display briefly. A new battery, out of the box, will generally read around 12.6 Volts. A fullycharged battery should read between 12.6 Volts and 13.5 Volts.
“- - -” indicates test in process, please wait.
ELK - BLT
4. The Mhos (internal conductance) reading of the battery will display within 6 seconds.
ON NEW INSTALLATIONS:
4a. Record the Mhos reading and the date of test on the test data labels or on the battery housing using a permanent marker.
ON SERVICE CALLS OR INSPECTIONS:
4b. Compare the latest current Mhos reading to the original baseline Mhos reading previously recorded. Then calculate the
percentage difference between the baseline and the current Mhos reading (the decline). If the Mhos has declined to 71% or
lower from the baseline Mhos reading the battery should be replaced. NOTE: If a calculator is not convenient then use the
Battery Mhos Reference Chart on the back of the BLT to locate the value closest to the baseline recorded on this battery. The
middle and right hand columns represent the value at 81% (weak) and 71% (replace) respectively.
E.G. Baseline - 180 Mhos Weak - 180 Mhos X .81 = 145.8 Mhos Replace - 180 Mhos X .71 = 127.8 Mhos
NOTE: No standard Mhos values exist for any battery size or brand. In some cases, different production batches of
the same brand battery will produce different readings. RARELY will any “similarly rated” batteries from different
manufacturers have the same baseline. Therefore, to accurately judge the remaining life of a battery it is absolutely
critical to have a recorded baseline for each battery that you use.
The Battery Mhos Reference Chart chart on the back of the BLT displays numbers equating to Mhos readings for
common security industry battery sizes. It is also based on a battery’s ambient temperature being at 72 degrees
fahrenheit. This temperature assumption covers many environmental situations, including cold basements or
unoccupied buildings, since the battery will be kept warm by the recharging and by being inside the electronics
enclosure. However, because cooler temperatures can significantly lower the Mhos reading of a battery, this
instruction manual has a more extensive Mhos chart with columns for evaluating batteries that are being adversely
affected by 62F, 52F, and 42F degree environments. Also see How Temperature affects a Battery
Automatic Shutdown
If the BLT is left connected to a battery for more than 30 seconds after the test is complete, it will automatically shutdown to
conserve battery power. Disconnecting and reconnecting a test lead will restart the test procedure.
Instructions
ELK - BLT
How Temperature affects a Battery
Generally speaking, temperatures below 72F degrees tend to slow down a battery’s internal activity, causing a significant decrease
in the Mhos (conductivity) reading as the temperature falls. Therefore, cool temperatures (not below freezing) will tend to prolong a
battery’s life. Temperatures above 72F cause a battery’s internal activity to accelerate, but with only a slight increase in the Mhos
reading. Warm temperatures will tend to dry out and degrade a battery much faster than normal.
72 F degrees = 0% no adjustment 52 F degrees = 87% (13% degrade) of normal Mhos
62 F degrees = 92% (8% degrade) of normal Mhos 42 F degrees = 82% (18% degrade) of normal Mhos
Battery Mhos Chart
for various Temperature Environments
72 Degree F Environment
Ideal Conditions
Baseline
Mhos
20 16
25 20 18
30 24 21
40 32 28
50 41 36
60 49 43
70 57 50
80 65 57
90 73 64
100 81 71
125 101 89
150 122 107
175 142 124
200 162 142
225 182 160
250 203 178
275 223 195
300 243 213
350 284 249
400 324 284
450 365 320
500 405 355
81%
Mhos
Weak
71%
Mhos
Replace
14
62 Degree F Environment
-8% degrade
Baseline
Mhos
20 15
25 19 16
30 22 20
40 30 26
50 37 33
60 45 39
70 52 46
80 60 52
90 67 59
100 75 65
125 93 82
150 112 98
175 130 114
200 149 131
225 168 147
250 186 163
275 205 180
300 224 196
350 261 229
400 298 261
450 335 294
500 373 327
81%
Mhos
Weak
71%
Mhos
Replace
13
52 Degree F Environment
-13% degrade
Baseline
Mhos
20 14
25 18 15
30 21 19
40 28 25
50 35 31
60 42 37
70 49 43
80 56 49
90 63 56
100 70 62
125 88 77
150 106 93
175 123 108
200 141 124
225 159 139
250 176 154
275 194 170
300 211 185
350 247 216
400 282 247
450 317 278
500 352 309
81%
Mhos
Weak
71%
Mhos
Replace
12
42 Degree F Environment
-18% degrade
Baseline
Mhos
20 13
25 17 15
30 20 17
40 27 23
50 33 29
60 40 35
70 46 41
80 53 47
90 60 52
100 66 58
125 83 73
150 100 87
175 116 102
200 133 116
225 149 131
250 166 146
275 183 160
300 199 175
350 232 204
400 266 233
450 299 262
500 332 291
81%
Mhos
Weak
71%
Mhos
Replace
12
ELK Products is not responsible for misprints or errors. The Mhos baseline values are benchmarks created from fresh samples of batteries. Be aware that if you find consistent,
minor variations in readings from multiple samples of a battery, it’s likely due to manufacturing differences.
Recording Battery Readings
The baseline Mhos reading of a new “fresh out of the box” battery may not be as high as the same battery after it has been sitting
on charge for at least 24 hours. If the reading is considerably lower than what you would expect then try charging the battery for at
least 24 hours, then retest.
Battery performance degrades over time due to use and abuse, and may be impacted by many factors like depth and frequency of
discharge. The higher the Mhos value the more current the battery can deliver. Therefore, a new 7 amp-hour battery will have a
higher Mhos value than a new 4 amp-hour battery of the similar construction.
Generating an Average Baseline
Start with 2 or 3 fresh new batteries out of the box. The battery voltage should be around 12.6 Volts or higher. Place the batteries
in service (on charge) for 24 hours. Remove them from charge and measure the Mhos reading of each one. Average the readings
together. This will be the baseline number that you can use for estimating battery decline. However, there is no substitute or
shortcut that can match the accuracy of actually measuring a baseline for each individual installed battery.
Instructions
ELK - BLT
Accumulating Trend Analysis over a Period of Years
Trending of periodic Mhos measurements can yield valuable insights for estimating the remaining life of the battery. Suppose that
a battery has been in service for three years, and that the BLT measurements after the first year was 90 Mhos, 85 Mhos after the
second year, and 80 Mhos after the third year. Since the battery is still at 80 Mhos and is dropping an average of 5 Mhos per year,
it is highly likely that this battery will not need replacing before the end of the fourth year. On the other hand, suppose that the
readings were 90 Mhos after the first year, 82 Mhos after the second year, and 70 Mhos after the third year. The rate of decay has
increased from 8 Mhos to 12 Mhos per year. This indicates that although the battery is still serviceable, it is degrading more and
more rapidly. It is unlikely that this battery will be serviceable for another year. Under these circumstances, either the battery
should be replaced early or the service interval should be shortened to catch this battery before a system failure.
Why Mhos instead of Amp Hour
The BLT measures the Mhos (conductance) of a battery using an AC impedance measurement algorithm. Every battery manufacturing
process produces a slightly different conductance value for a given battery size. Elk Products elected to display consistent,
accurate Mhos (conductance) values, rather than just estimated Amp Hour values. The only accurate method for measuring a
battery’s Amp-hour capacity is with a long discharge test, which actually decreases the life of the battery. Estimation of Amp-hour
capacity without a discharge test is a complex error-prone process involving the conductance value, the battery state-of-charge, the
voltage, the temperature, and the many varying design and production variables for each battery type. Ordinary testers which
measure static criteria or Amp-hour are inherently inaccurate across varying battery designs. In contrast, extensive testing has
proven that when the conductance of a charged battery is tested and has declined to approximately 71% of its full-capacity
reference, the battery is unlikely to deliver its rated capacity and should be replaced.
Is Mhos relational to Cold Cranking Amps?
No, the BLT is designed to measure the conductance of a battery at frequencies indicative of the capacity of a battery in Amp-hour.
Conductance measurements for estimating the Cold Cranking Amps for starter type batteries are at a much higher frequency.
Although the measurement techniques are similar, there is little correlation between the Cold Cranking Amps measurement of a
battery and the Mhos reading of the BLT, or vice-versa.
Using Mhos to Estimate Battery Life
The Mhos reading of a new battery out of the box will generally not be the same as that of a fully charged battery. This is due to
the plates not being totally formed during manufacturing. Once the battery has been on charge for some time the plates will finish
forming and the peak Mhos reading will normalize. For standby batteries, peak capacity is normally reached after about three
months on a float charging system. For cyclic use batteries, full capacity may not be reached until after ten to thirty cycles,
depending upon the depth of discharge and the charging method.
If a new battery has been in storage for an extended period, say over six months without being charged, plate oxidation from selfdischarge will occur, causing a decrease in the Mhos reading. Plate oxidation also occurs in standby batteries during a power
failure, particularly if a battery remains in a highly discharged state for an extended time period. Plate oxidation is unhealthy and
can destroy a battery’s capacity. Once a battery is weakened by plate oxidation, it is difficult to recover full capacity without special
charging or conditioning methods. In some cases a battery will recover and pass a test after being recharged. However, a second
test should be performed a few days later after recovery to accurately assess the overall life of the battery.
The average life cycle of a sealed lead-acid battery in standby use on a float charge is 3 to 5 years. At this point in its service life
the battery Mhos reading has generally reached a point of 71% or lower of its original baseline reading. The battery should therefore
be replaced since it is no longer considered serviceable.
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