I would go for a 5v power supply like a high power USB charger or a 5v-5A cheap PSU from ebay and some lithium charger boards:
http://www.ebay.com/itm/10Pcs-Lot-TP...ht_3689wt_1125
http://www.ebay.com/itm/5V-Mini-USB-...ht_6344wt_1145
These chargerboards have a full automated single chip lithium charger. If you know the chip you can find the specsheet to help you to change the charging current when needed. (mostly a resistor)