a very simple and "old school" way of recharging a set of series NI-??? things is to do a simple slow charge. i have used that method for years on multiple ni-?? devices , and never had any long term issues.
when/if you cant afford a $$$ hobby charger, that has an good series alogrythm for charging, then Slow Lame dum charging is very effective and cheap.
just stay below 1/10th C for charging , and prefer to do that for 14-16 hours. it will blance out ok and work fine.
its also a good way to have a cradle or in-device charger, when there is no access (or needed) to the batteries, and you can have multiple devices slow charging with $5-15 wall warts, which covers the issues of TIME taken to accomplish the slow charge.
a wall wart that is just the right voltage will also taper the charge neer the end of charge, making it pretty safe , and did i mention CHEEP
you might not want to do that for a hotwire with a mad discharge rate, but for everything else it works good.