If you're like me and don't like spending money then a cheap manual wall charger is best. Find one with approx 300-600 ma and for 6-12 volt batts. Remember all those old power supplies, dc adapters for phones, games, electronic devices? You may have what you need already. I've got a big box full of them.
If you've already used the 100 ma for many hrs then the forming chare has been done and can be forgotten. The 977 will keep the cells in balance. I'm wondering if it is even necessary now. You've already done it , it sounds like.