What is a reasonable time to expect your batteries to last before you have to replace them? I have both XL and regular manuals. I'm pretty new so any that have crapped out have been replaced no questions asked, just want to know what I should expect. If there happens to be a sale on all items before the end of the year I'll probably order a few more. Thanks for the latest sale on juice and carts - I feel like I have enough carts to last a lifetime - know it's not true but for a newbie it's quite a stock pile