Several years ago, I took a stab at doing a life-long desire -- fly remote control model airplanes. I found that the hobby had been totally revolutionized by Li-Po battery technology which allows reasonably long fly times and great power without the terrible noise of the gas glo-plug engines. No fuel to buy. Just recharge the LiPo pack -- with very special and sophisticated chargers.
In the process I learned about the limitations of Li-Po batteries.
In particular, if they are overcharged to more than 4.2 volts per cell (with maybe a .1V or so margin) they are toast. Also if they are discharged below about 3.0V per cell, they are toast. There is no recovery to the battery at all. All LiPo battery packs (and/or their dedicated charger) have solid state circuits which monitor the charge and discharge voltage. This type of circuitry is embedded in your cell phone, digital camera, laptop computer etc. If either the plus or minus threshold is reached, the charge or the discharge is terminated before damage to the cell/cells occurs. LiPo's maintain their charge very well for extremely long periods compared to other types of battery. Self discharge rate is low. Number of discharges and re-charges is very high. An RC battery pack has taps for each cell. Discharge is in series, but the taps allow each cell to be individually charged to the 4.2V maximu. The pack is then balanced.
Nominal voltage for a single LiPo cell is 3.7v So a power tool at say 15V or so would have four cells in series. Like any battery type, LiPo cells are available in lmany maH sizes. And also maximum rate per unit of time of discharge varies. A couple of tiny 100mah LiPo's weighing only 1.5 ounce eac will power a tiny indoor ultra rc plane. Or several huge LiPo's in series will power an RC airplane with a 6-7 foot wing span enough that the thing can even hover vertically for a while.
Reading the threads, maybe the inverters are disrupting ability of the charge control circuitry to function right? The LiPo's might get overcharged and ruined?
If so, MaineSail's last sentence about using instead a 12V charger does seem like the best safe idea for recharging power tools on a boat.