It is important to choose your battery system and stick with it. I selected Makita because that's what my contractor uses to make a living. I recently took advantage of my state's green lawn care rebate to purchase a heavily discounted Makita lawn mower which -crucially- came with 4 big batteries that fit all my other tools.
It is also important to realize that a pair of 18v Lithium Ion batteries can deliver more wattage than a regular (USA) household electrical outlet, especially while using an extension cord. The Makita chop saw is a great example of a battery product that is actually superior (IMHO) to the corded version.
Makita's fast chargers have a built-in fan that cools down a hot battery and maintains optimal temp during the charge cycle. Even my oldest batteries still work great.
It is also important to realize that a pair of 18v Lithium Ion batteries can deliver more wattage than a regular (USA) household electrical outlet, especially while using an extension cord. The Makita chop saw is a great example of a battery product that is actually superior (IMHO) to the corded version.
Makita's fast chargers have a built-in fan that cools down a hot battery and maintains optimal temp during the charge cycle. Even my oldest batteries still work great.