Low self discharge batteries for ps1 and/or early ps2?

First off, I don't know anyone who knows the actual charge rate built into the engines. All we can go by is the External Charger MTH sells.

The MTH replacement PS-1 NiMH battery is 120mAH @ 8.4V, The NiCD battery is 700mAH @2.4Volts.

NiMH charging rates are much more restrictive than NiCD rates.

The instructions for the PS-2 (NiCAD) charger MTH sells tells you to charge for 12 hours to ensure a full charge.

This equates to a 58mA charge rate which is well beyond NiMH standard charging rates and beyond the max Fast Charging rate for the Battery you linked.

The Stated Charge retention on the datasheet is highly dependent on temperature.

Hot storage will reduce it drastically but in your home you should hold 60% of a full charge after 3 months.

This is very good for a NiMH or a NiCAD.

A standard NiCd would lose more than that in the same time. (Max loss 30% of remaining charge per month per wiki and my memory)

NiMH batteries are used for greater power density for a given wt and size, not for charge or discharge rate, Retention over time is secondary but good.

We need power storage over time VS power density.

HOWEVER, WE DARE NOT CHARGE THEM TOO FAST, FIRE HAZARD !!!

Bottom line: I would avoid the battery you linked, the charge rate in our trains is likely too high and will cause a very nasty fire (the kind you cannot extinguish and producing lots of Toxic smoke). The charge loss in storage is better than a standard NiCAD and weight really does not matter so it has qualities we want over the stock battery but the Fire Hazard over-rides.

While the battery charging circuit in the locomotive may exceed the 40ma maximum rate slightly, I think there is a very low possibility of a fire.  Also, NIMH batteries don't have the same type of fire hazard as Lithium based batteries.  There is nothing flammable in a NiCAD or NiMh battery like there is in a Lithium cell.  Fires with the other battery types are usually caused by short circuits.  A modest over charge of a NiMh battery normally results in a reduced product life.

I just did a quick bench check with a 5V PS/2 locomotive that I have apart right now.  With 14 volts on the track and a 8.4V NiMh battery reading 7.7 volts open circuit, the charging current was 27 ma, so I'm thinking the charging rate for the PS/2 electronics isn't an issue.  I don't have any PS/1 stuff here right now to test.

Thanks for the replies.

I'll have to test the current on a ps1, but can't get to it today. John, can you tell me how to do this test? I'm assuming I would power it from the track and then touch the battery terminals with multimeter leads? I don't want to try it if I'm going to ruin the delicate ps1 electronics. Thanks. 

Any thoughts on the other aspect - the retention of a charge?

Russell cited a 60% charge after 3 months, less than the advertised amount, but noting that it is still fairly good.

Obviously, if there is a fire hazard it is out the window. But, is there anything in the data sheet that makes it more susceptible to a fire than any other Nimh, including the ones from MTH?

Thanks again.

Actually, I measured it using a Fluke DC ammeter between one of the battery terminals and the locomotive charging terminal.  The ammeter should be in series with the connection.  Connect the battery to the locomotive with one of the snap-on connectors, then connect the meter between the unconnected locomotive and remaining battery terminal in series with the connection.  The battery should be partially discharged for the test so you get the standard charging current.  Give it a minute to stabilize and then take the reading.

Good point John, I had NiMh and Li-Ion mixed.

Li-Ion is even more picky about charge rates.

I'm surprised by the charge rate you got considering the projected rate of the external charger. Then again, perhaps the 12 hr charging is a large overcharge time wise for ensuring full charge.

At low charge rates overcharging NiCADs or NiMH is not too serious.

Russell, I can tell you stories about Lithium batteries, I've consulted for several companies that make large Lithium battery arrays.  When they burn, they are truly impressive!  And you're right about those, there's no putting them out by conventional means, usually they just let them burn themselves out. 

Ask Boeing or Cessna Aircraft!  Both have had major incidents with Lithium batteries on aircraft!