Dewalt Batteris

[John Force]

Dewalt battery questions:
1-My circular saw takes 18v XRP batteries (just died). Can I use my drill's 18v (not XRP) battery without hurting it?
2-When the XRP died, I did a little research and according to Dewalt, I should leave the batteries on charge all the time (these are nicad batteries with a Dewalt "tune up" mode charger). Should I leave my Hitachi Lithium Ion batteries on charge all the time also, or cycle them every few months or so like I have been for the last 18 months?
Thanks in advance for the help.

[Van Huskey]

I will give you a bump and say I would not personally leave any Lithium Ion battery on a charger unattended much less all the time...

[Tom Cornish]

Nicad batteries discharge fairly rapidly over a few months. Keeping them on the charger will keep them topped off and ready to go, but will shorten their calendar life a bit compared to letting them discharge naturally and recharging them just before you need them.

Lithium ion batteries have a much lower self discharge characteristic (assuming there isn't some other flaw in the tool that drains power like some Ridgid tools) and hold 90% of their charge for several months. There shouldn't be any need to keep the batteries on the charger for them to be ready to go.

You can destroy Lithium batteries either by over charging them or over discharging them. Most tool systems have mechanisms that prevent this - intelligent chargers that won't overcharge, and cutout circuits that stop the tool when the pack reaches the end of the safe discharge curve. It's still possible on some tools to hit the trigger again and drain the pack more - that's a potentially expensive bad habit.

A good nicad pack can last 5 or 6 years with care. There are reports of people resurrecting shot nicads by zapping them with DC from a welder. I haven't tried this, and am a little afraid to.

Lithium batteries have a maximum cycle life of 300 to 500 cycles. The electrolyte also starts dissolving the electrodes, which means that even if you only charge your batteries once per year, after some period of time the batteries will be shot from age rather than usage.

Some laptop manufacturers actually have two lines of batteries for their devices - regular batteries that are good for one to two years, and "long life" batteries that have a slightly lower energy density, but are supposed to last 3 to 5 years.

On the tool side of things, if you believe Dewalt's marketing info (I do), their Nano batteries will outlast most other lithium batteries in the calendar life arena. Their cells are 2.3Ah compared to most of their competitors' 3.0Ah cells, but a year into the life of the tool, the non-Nano cells will lose a large percentage of their capacity while the Nanos will keep on going (theoretically).

I have owned the Dewalt 36V nano kit since May 2007. One of my packs died in the first year, and Dewalt replaced it (actually it took me over a year to get around to talking to Dewalt, so they went above and beyond to take care of me replacing a 2 year old battery on a one year warranty), the other is still going strong. I used that kit to build my current house - fairly heavy usage for 2+ years. I had a good enough experience to buy the 18v Nano drill and driver, and so far I've been very happy.

The good news is prices are starting to come down on Lithium packs. I also have a Festool T15+3 (not sure what battery chemistry - probably not the same as Dewalt's A123 batteries), but decided to give it a try considering replacement batteries even from Festool were less than $100.

If you like your saw and want to continue using it, you may want to give one of the new Nano lithium batteries a try - they will fit your current 18vXRP tools, however you will need to get a new charger. Chargers can be had pretty inexpensively as there's a secondary market where tool kits are split up and the pieces sold on Ebay and other places. I bought my second charger for $20.

[Dave Houseal]

The regular batteries are perfectly fine in XRP tools and vice versa. The XRP batteries just have a higher capacity. So your saw won't run quite as long, but it will run just fine.