I bought a new highter current ni cad for my makita; however, the

You should not try to piggyback batteries. People that claim all these tricks to bring back dead batteries are not being forthcoming.
The charger is designed to charge battery that in working condition, if battery is bad, there is no magic mouse milk for it. If you are using Ni Cad battery they have a very short working life, and if left on the charger, it does not help them, it will degrade battery quickly. I would use on Lithium ion battery and forget Ni cad.. i disposed of all my battery tools that used nicad and replaced with with a new tool. Makita is a very good brand and of high quality.
Don't believe everything on you tube, anyone can post a video whether they are knowledgeable or not. You can go on you tube and claim to a nuculer engineer with ll kinds of free electricity for your home does not make it true.
I've included a link to manual.
https://images.homedepot-static.com/catalog/pdfimages/35/35393127-7c0b-4668-8609-9104ae7cc187.pdf

Lithium Ion batteries don't charge the same way ni-cads or ni-mh do. You need a lithium ion specific charger to charge them. (Some chargers do multiple types.)

Hi,
It sounds like the problem is the battery. It sounds like there are shorted cells in it so that it starts to draw too much current from the charger and the charger shuts down as a safety measure.
I hope this helps,
Happy New Year,
Mark

Makita makes two 12V Ni-Cad pod batteries: Battery 1222/2.0Ah (PN: 192598-2) and Battery 1220/1.3Ah (PN: 192681-5). Makita's universal charger (PN: DC1804) will charge any Ni-MH or Ni-Cad pod or stick battery from 7.2V to 18V.

Join the battery collectors club. I have 25 batteries, 12 guns, I quit buying the batteries, I found it cheaper to buy the gun with new batteries and charger once a year. Cause they don't even last that long. I have tried different brands too all the same. Got batteries?? Sure do.

you got me. check your suppliers line of supply . I runas many lithium with a 10 man crew and we are punishing, to this day not a problem. we did have a problem using the smaller batteries, but no problems with the larger BL1830 batteries

I "m 99% sure Milwalkee is the only company that is interchangable..lithium ion and Ni cad ......... the new Milwalkee Lithiom ion chargers will chare both lithium and nicad, but the ni cad chargers will not charge lithium ion. Thanks Hope this is helpful!

What type of battery pack Ni-Cad? if not then you don't have to dis-charge it, only Nicad's need to be run flat.

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