Plugged my Makita Makita 7.2 18 volt ni-mh or li-ion battery Charger into 24O volt by mistake HELP

SOURCE: Makita DC18RA Li-Ion 18V Battery Charger

Most likely, but unless the transformer blew, which is somewhat unlikely, a good repair shop should be able to fix it. Basically the charger unit is a transformer, some diodes to convert ac into dc, and some sensing circuitry to tell you when the battery is done charging. Diodes and sensing cisrcuitry are commonly available parts and not expensive. Transformers are expensive. Even if you get it repaired youll still need an adaptor to convert from the mains 240 to the 120 that the charger wants to see. Get one with a high enough wattage for the charger. Wattage is printed on charger base.

SOURCE: makita dc1804f charger will not charge new i-mh 1834 18v battery

I think your tryiong to charge NIMH batteries oon a charger designed for Lithium Ion batteries. With all the new style batteries such as NICAD, NIMH and LI-ION, charging becomes difficult. Most chargers pre NIMH and LI-ion, were designed for NICAD's. The best advise, match your batteries with the correct charger

SOURCE: problem charging makita batteries 18v

Unfortunately, Makita’s li-ion battery packs have a design flaw. After having the same problem with my two batteries, I took it apart and saw the problem immediately. You see each battery pack has ten li-ion battery cells and a circuit board with a memory chip witch holds the charging history of the battery pack. But that memory chip constantly draws power from 2 of the 10 batteries. The current it draws is very small but if you consider it over 8 month or more, the power drain becomes very significant. You end up with a battery pack with 8 still fully charged battery cells and 2 drained battery cells. When you put this battery pack in the charger, it detects weak battery cells, assumes they are defective and refuses to charge. To avoid this problem you should charge your battery pack often, even if you haven't used it, every two months should be ok.
I suspect that Makita doesn’t make these battery packs, they make power tools, good ones too. Buy Makita should definitely have a few words with their supplier before they become a liability!

SOURCE: makita cordless driver drill model-6347d.

You say will not stay charged? Over what time period? Are you aware Nicad and NiMh rechargeables discharge naturally at 1% per day so where does that leave your power tool after 3 months? Furthermore they only have around 1000 charges in their useful life so you can immediately see how these tools are not for intermittent(ie handyman) use.

SOURCE: batterie Makita BL 1830 ne recharge plus

Pardonnez moi parsque ma francais est tres mal! If you have been a bad boy and managed to short the battery by using it for non-proscribed purposes, the fusible link will blow (kind of like a fuse) To fix it, open up the battery (use a Torx 10 security bit, or a small flathead in a pinch) On the battery connection nearest the spring-loaded white catch there is a small bridge of metal with a hole in the center. If this is melted you can solder it back together by sanding the two pieces and putting a glob of solder on them. This will void your warranty (duh!) and remove the battery's fuse protection, but it WILL work again. If the link is intact and nothing else is obviously wrong, you almost certainly have a bad cell. I recommend pulling out the bad cell ( it will be the one that does not read between 2.5 - 4 vdc) and replacing it with one from another dud battery- this requires some fudging and re-soldering. Or do what I did, pull the cell, toss the electronics and the short pink wire, add a cigarette lighter socket and voila! you have a portable power supply giving around 14 volts. Charge it up by wiring two cigarette lighter male ends together (check polarity , + to + and - to -) and plug it into your car, but only while it is running or you will be charging your car battery with it! Hope that helps.
Matt Binns GiantGlobes.com