My friend has a DX50, and it works great on eneloop rechargeable batteries. Some people say their DX lasers don't work well on rechargeables (The DX lasers are manufactured by random factories so there are a lot of different DX50s out there) so you may have to stick with regular alkalines. But give eneloops a try, they are great batteries.
If your talking about non rechargeable, name brand alkaline s for if you want a longer lasting one that would give more power get energizer e2 lithiums.
If you want rechargeable which i recommend due to the cost it saves get eneloops, they don't discharge themselves like most rechargeable batteries do.. ive been using mine in my x65 and they work wonderful.. and you can charge them with any ni-mh aaa charger