HOW-TO: Measure battery health

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Simple method to monitor your battery performance over time

Ego is fairly young in terms of Outdoor Power Equipment (OPE), and there isn't a lot of run time data out there for how their batteries will perform over a few years.  Ego batteries carry a 3 year warranty. 

Knowing the health of your battery can aid in diagnosing problems.

Equipment Needed:
(1) power meter (Kill-a-watt is a popular one on Amazon)

Much like checking how many miles per gallon (MPG) you vehicle is getting, you could top off your battery, then use it, and then measure how much energy it takes to re-fill.  Of course there will be times that you will not run you battery down until it stops (e.g. blinking RED, and the tool won't turn on anymore).  And as long as your notes denote that, you can account for it in your trend analysis.

No piece of equipment is 100% efficient, and while we could develop an elaborate setup, the amount of effort required will not likely change the overall outcome.  Therefore, as long as one use the same power meter, the lifetime data will be pretty close.

I'm going to analyze two batteries: 1) The Ego 2.0AH (#1) made back in 11/2013, and 2) Kobalt 80v (#1) made back in 12/2014.  First the Ego, even though this battery is over 3-1/2 years old, it is still above 90% capacity.  The Kobalt on the other hand, I have used that battery hard, with the 80v chain saw, that one is either 81% if you use the full voltage, or 90% if you used Kobalt's posted capacity (calculated using 3.6v instead of 4.0v).  So I might want to dig up that receipt for the Kobalt and haul it back over to Lowes for a replacement.

This might be a stretch, but seeing your battery USAGE (kilo-watts hours to recharge) go up over a season might be a good reminder to sharpen your mower's blade.

Is this necessary, not likely.  Will it help with a warranty claim, probably.  Am I being a geek, absolutely!

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(a)Typical Engineer

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Posted 12 months ago

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I do something similar; charge battery fully, deplete fully using blower set on lowest speed, charge fully using the standard charger, record total charging energy.

This is just a test, I don't monitor weekly energy usage. I use the blower set to low speed to get a consistent discharge at a low rate that doesn't heat the battery.

The problem with assuming the actual capacity of the battery is, we don't know how efficient the charger is nor do we know how efficiently the cells take a charge. The charger has two fans to pull heat during the process.

I believe this method would be useful to monitor a battery's relative capacity over time, or relative capacity to other Ego batteries tested in the same way. The same charger unit should be used in case there are unknown changes made over time.
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FYI - I'm currently measuring  420 watt/hrs to fully recharge a 7.5 AH battery (on the quick charger).
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Michael G

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I found this post interesting. Here are my initial results:

Battery    kW-HR
2.0            .11
2.5            .14
5.0            .29
7.5            .44