||12-03-2014 04:33 PM
NiMh batteries will work fine, some are inexpensive and a very viable answer IMO. That said as Pete noted the Sierra card is not designed to charge batteries per say, it employs a regulated voltage output to charge the battery, nothing is in play to limit or recognize when said battery is fully charged. Nor does it matter what technology the battery is, the Sierra card just continues to charge no matter what... I use inexpensive 6V NiMh radio control aircraft RX batteries in several engines equipped with Sierra Sound cards. I charge the batteries with a separate or remote AUTOMATIC or Smart battery charger, this also helps to cycle/maintain the batteries.
NiMH batteries need to be form charged or fully cycled; i.e, charged/discharged at least three times to realize their full capacity and voltage. Thereafter trickle charging is fine for nor more than 24 hour period in most cases. It really depends on the output of the charger and the battery capacity. Simply divide the charger output by hours/minutes to factor a typical recharge time interval. For example: 120mAh charger and a 600mAh RX battery is in hand.
.6Ah/.12A=5 hour charge time.
600mAh/120mAh=5 hour charge time.
Keep in mind the above is reflective of charging a completely expired battery, not a partially discharged battery. That said low output trickle chargers can be allowed to run wild for a maximum IMO of perhaps 24 hours, this allows cells to balance charge themselves without the detrimental heat associated with higher current/amperage charging. Prolonged trickle charging is NOT a good thing...
Another consideration is NO battery at all, some of us have employed SUPER CAPCACITORS in lieu of batteries. These charge up when the railhead is powered and act much like a battery thereafter. The good part is you never need to charge them.