Tale of the Rechargeable Battery
There are strange things done in the midnight sun
By the men who moil for gold;
The Arctic trails have their secret tales
That would make your blood run cold;
The Northern Lights have seen queer sights,
But the queerest that’s ever been said,
Was that night on the marge of Lake Lebarge
My HT battery went dead.
(My apologies to Robert W. Service and his Cremation of Sam McGee; a favorite of mine, and somehow fitting here.)
I think we all have rechargeable battery tales, don’t we? For nearly four decades now, ever since my father bought a military surplus ni-cad battery array, I’ve been in a constant battle with batteries. There is perhaps some irony in the root of those two words, battle and battery, which are French in origin.
There are many myths, not-so-sound advisories, and nutty ideas about rechargeables. These days, I ignore them all and go with what works well for me.
Here are a few of my conclusions:
- Keep your batteries “topped off”. In other words, recharge often and recharge fully. How often? Every day, if possible, but for sure never go longer than a month. Have you noticed that those solar lights in your yard will run for two or more years, often 700-1000 cycles, because they diligently follow this rule (of course, they have no choice.)
- Use a good quality charger. If it’s not providing a complete charge, or if it charges with too much current (battery gets really hot, causing internal evaporation), you need to find a better charger.
- Avoid complete discharge, if possible. Sure, you will get all kinds of advice on this point. Just keep in mind that you’re using a reversible chemical reaction that emits heat and deteriorates “at the edges” of the curve: full discharge and over-charge.
- Use a good battery tester to confirm that your battery has reached the end of its life. I don’t know of any good battery testers, so I made my own. It’s a shunted milliamp-meter that pulls nearly full current for a very brief period. This technique makes the condition of the internal resistance quite obvious.
The second point is worth expanding on. Some battery chargers are devious. The worst ones, like on my cheap Ryobi cordless drill, never stop charging, eventually drying out the electrolyte. I lost three drill batteries until I noticed their sly trick (selling more batteries.)
Most average battery chargers will allow a battery to go dead even while it’s in the charger. They may do a good job charging, but once done, the battery will begin discharging on its own. It’s aggravating to take a battery out of the charger, only to find it’s dead. (Note this will happen on many laptop computers too.)
A good charger will top off the battery with regularly timed cycles, or provide a trickle charge. However, obtaining the correct trickle charge is non-trivial, and most chargers won’t do it properly. Actually, I don’t know of any, so if you own one (or built one) let me know.
Also, keep in mind that a dead battery pack does not mean all of its cells have gone bad. I often break open dead battery packs and test the cells separately. It’s usually just a single cell that died (1 in 6 or more) but most people replace the entire pack, costing $60-90. Another sly trick?
Anyway, I’ve written about this topic a few times in the past, and I could go on forever. You probably have your own special tales to tell. I invite you to post them in the comment section.