Ideal Charging Strategy for Lithium Cordless Drill Battery

The manual of my Black & Decker cordless drill battery says to charge after every use to maximize the battery’s life. This would essentially keep it fully charged, for me that is, because I tend to use it very briefly. I understand that the most important thing is to avoid fully discharging, but is keeping it topped up really the best strategy? I ask because I read somewhere that lithium batteries should ideally be discharged to 50% before charging, because the total run time is better than, say, recharging every time it’s 90% charged. This also implies that keeping it topped up at all times is not the best way.

Is my understanding on this topic accurate? Or does the ideal strategy differ depending on the particular lithium battery? Supposing that I’m wrong, how exactly should I charge it? Keep it topped up like the manual says?

It depends on use. Li-Ions do not really self-discharge, they lose capacity. Permanently. High and low State of Charge, and elevated temperatures, both speed this. Really, you’re best off keeping the power tool battery something like 20-80% charged in good temperatures, but that leaves you 60% of the total capacity ‘available’ for use.

If I don’t need too much of its capacity “available” for use at any given time, 20-80% is better than keeping it 100%, charged as the manual recommends. But my next question is if anywhere in the 20-80% range is equally ideal, in theory? That is, would 20% be better than 80%, or would the difference be negligible? I recall reading on here that NiMH batteries should be ideally stored fully discharged, as long as they are recharged ~monthly. Of course, NiMH isn’t lithium, and the advice could be wrong, but some of us who don’t actually use our batteries might care, as silly as it seems.

I’ve been using a 12v bosch litheon system since it came out. I generally use it and toss it in the bag unless I plan on doing more work the next day, in which case I’ll top off the charge. Back when I was doing commercial electrical work I mostly used 18v nicad tools, and the 12v lithium stuff only got brought out for renovation work above ceilings and a few other odd jobs. Those were kind of sporadic and the 12v lithium batteries spent months at a time fully charged, nearly discharged(when it was convenient) and being recharged every day.

They’ve been going strong for 5 years and nowdays mostly get used around the house on a weekly basis. The runtime does seem a bit shorter than new but not enough to be a bother. A single 1.3ah battery in my first gen pocket driver had enough charge to drive 40 or so durock cement board screws when I did a shower stall last year with a bit to spare. When bosch releases the 2ah 12v Ryobi power tool batteries hopefully this year I’ll be expecting the same or better from them at the 5 year mark.

Storing at lower voltage is better, but it’s been my experience that they handle being stored at full charge pretty gracefully. There is something to be said about being able to toss the tool in your bag, grab it a few months later and have it ready to go without needing a recharge(in my experience this kills nicad batteries pretty reliably). That said I normally don’t recharge unless I have work to do and I see the power drop/capacity gauge at 1 bar.

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