Heath Zenith Hero Jr

I was amazed to find a local classified ad for a Hero Jr in the Saturday morning paper and soon after I was owner of a very clean Robot for a few dollars (about time I had that sort of luck). Unused for many years but just some cobwebs inside, no corrosion. No charger or remote control or cartridges or documentation unfortunately, but there is lot of technical info on the web I have found today. The old battery will not take a charge using my car [translation - auto] battery "trickle" charger, so I'll have to wait 'till next week to buy a new 12V 3.5A sealed lead/acid battery - that's how this Australian model was powered - not like the 6V batteries described on the web pages for the Hero Jr. And I don't have a 12V PSU to power it up with in the meantime. Am I using an appropriate re-charging device? And could I use the trickle charger itself as the PSU for testing? A multimeter reads about 13V across the terminals when it is powered up, but with my minimal electrical knowledge I do not dare try something that could be fatal to the Hero. None of the Web pages mentioned how much this thing cost new (Feb 85 manufacture date I suspect by a sticker on board inside) and I am curious about that. If anyone has any warnings or "gotcha's" about working with this thing, I'd be glad to hear from you. Other than that, I can't wait - from the info on the web it sounds great fun. And it goes to show, however rare or unusual the item is - eventually one of them turns up here in Brisbane, Australia. Phil