Well, options is maybe a bit overstated :) From my very first Newton on, I had been using battery packs which I can recharge with the Newton. But a couple of years back I changed my usage patterns so that I had the Newton pretty much all the time plugged in, and switched to Eneloop batteries, which I charged with a separate charger. Those batteries seem to be slowly dying now, and I’m contemplating changing back to internally chargeable batteries. This would fit my usage patterns probably better anyway, as I use the Newton nowadays mostly for journaling, idea collection and to hold reference data, not that much as an organiser which has to be switched on all the time.
Since my old battery packs are pretty much dead, I already ordered rechargeable batteries with solder tabs. Let’s see how the battery pack hacking turns out!