How long will it take you to reach 400 cycles if you charge to 100%? If it's several years than probably not worth it. If it's a year or two and you think you'll still own the bike at that point it's worth it to pay more up front for a bigger battery. Those upgrade prices aren't bad either. On the OEM e-bike side you're typically paying hundreds of dollars for those types of watt hour increases. The Luna Advanced chargers are all you need to charge to 80% and they run about $100.