Batteries

First if it has been sitting for a long period,test the voltage before charging. If it registers negative voltage it suffers from cell reversal and should be thrown away. After charging it should read around 8.4 volts DC. Then put the battery under a load by powering a few 12 volt light bulbs for example or a wirewound resistor. When put under load the voltage should not drop very much,then as it discharges it should drop in a linear fashion. If it drops suddenly from say 8.4 to 5 or something,the battery has developed a "memory effect" common to Nicads. If this does not happen the battery is probably OK but the above 2 conditions can develop later at any time later when used in the circuit. 

I do not know the answer to your first question,I think NIMH are OK and do not have the shortcomings of the NICADs. I use all BCRs in mine.

Dale H

Odd as it may seem, the first question is what is the output voltage on the lithium battery?  A so-called 9-volt NiCad or NiMh is normally 7.2,* which is inadequate.  A few are 8.4, which is fine.

Reason for thisis that the oriignal 9-volt batteries, either carbon-zinc or alkaline, had 6 cells each putting out 1.5 volts.  When the replacement rechargeable came out, they also had 6 cells, but a NiCad or NiMH cell is only 1.2 volts; nevertheless they were billed as 9-volt because they fit the same as the older 9-volts.  Some makes now use 7 cells.

I had said "lithium re-chargeable" but maybe it's NiMh I saw, that is out there, not lithium. I'm not sure, but they're all you can get now. Even Radio Shack does not sell the Ni Cad.

Yet, the MTH batteries were NiCad. Were they higher output voltages than standard, Radio Shack NiCads?

NiCads & NiMHs have the same output voltage, 1.2 volts per cell.  NiCads are said to have a lower shelf-discharge rate (how fast they run down just sitting), but they do suffer from memory effect.  A NiMH 8.4 actual volts is fine for the older PS2 units; the newer so-called 3-volt boards would take 2 AA or AAA NiCads or NiMHs.  The NiCads were alo environmentally unfriendly in landfills.

Jay,

I don't think you want to use Lithium batteries in your MTH engines. Most of them use a different charger than the others. Check with MTH before trying these. The 8.4 NiMh batteries work fine or if you plan to keep the engine for a long time, I would replace the battery with a BCR.

All new MTH Batteries are NiMH. The 5 volt boards use a 8.4 volt battery Part #BC-4000005

As Forest says.  Cad is not good for the envior, hence the shift to NiMH.

Any NiMH that is 8.4 volts will work fine.  G