I'm satisfied with the DeWalts, and you can get spare batteries for them at the box stores. They made a change about 4-5 years back. The original batteries just had the two charging terminals on them. Then, they added a 3rd small electrode between the big charging ones. The companion charger uses that 3rd terminal to measure the temperature of the batteries during a charge. The replacement batteries and charger lasted much longer than the original ones (in terms of # of charges). Sensing battery temperatures on NiCads (or nickle metal hydride batteries) has been around since the 70's (at least), DeWalt cheaped out and then had to make changes.
So, if I was buying new I'd go for a lithium system. If I was happy with my various DeWalt tools I'd check the charger/battery for the 3rd terminal. If you have it, just get replacement batteries (on line seems to be cheaper than box stores, but factor in shipping). If you don't have the 3rd little terminal, I'd still consider new batteries and a charger. I got new batteries and charger 5 years ago when we started the house, they are still OK. Not quite as much charge but they've seen a lot of use. The original two terminal only batteries lasted 5 years, but that was with infrequent weekend warrior homeowner use- nothing like the 20 months of house construction.
Pete