Rechargeable Batteries--Initial Charge

Read somewhere that 24 hours or so is the optimal initial charge time to ensure maximum rechargeable battery life.

Is this a myth?

Would such a long initial charge damage the battery?

In one case, at about the 12 hour mark of an initial charge, the battery was knocked loose from the charger but replaced within a minute or so.

Would this accident have any measurable effect on battery life?

Your answers will be much appreciated.

I don’t know much about this subject, but I suspect that the answer is going to be very different depending on the actual chemistry of the rechargeable batteries involved - are they lithium-ion, (common in laptops and cell phones, for instance,) nickel-metal-hydride, nickel-cadmium, rechargeable alkaline, or something else??

That’s what the instructions seem to always say, but I’ve never found it to be necessary. It’s not like batteries only work when they’re completely full, and you have to recharge every ten minutes.

It’s very different for different battery chemistry. For example, low discharge NiMH batteries are shipped fully charged.

I’ve never heard 24 hours, but generally instructions that I have seen tell you to fully charge the battery before first use. It usually takes 2-4 hours to fully charge. This is generally for cell phones and cameras, the devices that I replace the most frequently, and usually lithium-ion batteries IIRC. I can’t imagine any benefit to charging a battery past when the charger says it’s done, and certainly not to 24 hours. But as mentioned, I suppose this could be the best advice for some battery types.

NiCD, hell yes, 12-14 hour initial charge.

NiMH, hell yes, 12-14 hour initial charge.

Li-Ion, no, just charge til it’s full.

SLA, topping charge if desired.


If I may piggyback another question…

This site says:

Is this true? I’d like to have a battery so that I can learn how to use the deck (although I can use the a/c power supply, I’ll want to do some field tests), but I won’t actually ‘need’ audio until next Summer at the earliest. So if it’s true, there goes 1/6 of my shelf life.

Yes, Lithium Ion will degrade over time, especially if the voltage of the battery drops too far. You will almost certainly have a not insignificant number of bad cells.

Another point to consider is the charger. Different chargers have different degrees of smarts.

I think the days of one-size-fits-all rules as the OP cites are long gone, particularly when looking for “optimum” results. The best answer is “It depends on the specific charger & battery.”

This is what I heard from a dealer (may not apply to your situation): In complex electronics, there’s a chip that regulates battery power. The chip is what tells your electronics to display “low battery,” “full battery,” or shut off your device. The “full discharge, full recharge” advice is to make sure the chip properly recognizes your battery, and doesn’t shut your device off when the battery is still half full.

In my experience, rechargable batteries have a certain number of uses before completely becoming useless. For laptops, for example, they are generally rated from 1000-2000 uses (3-5 years) before needing replacement, cell phones are probably less. Therefore, you can keep a battery forever if you never discharge it (which kind of defeats the point of having a battery at all, imho.) My wife’s laptop, for example, has been plugged in since the day it was opened, and the battery still reports the same usage time on battery for the past 6 years.

No, lithium-ion batteries just die. A battery charged 100% and kept room-temperature will still lose 20% capacity per year. Actually, a 50%-charged battery does better, but lithium still has fundamental shortcomings. Ni-MH has advantages in that respect.