OptiMate 4 Dual Program includes two charging programs; program 1 is for direct charging of a battery, program 2 allows safe and unsupervised charging through a BMW motorcycle’s CAN-bus controlled 12V socket. OptiMate 4 Dual Program tests before & after charging and can recover a ‘dead-flat’ battery from as low as 0.5 Volts. There are clearly quite a few differences in terms of features, most of them favorable for Optimate 4, but it's worth mentioning that Optimate 2 is meaninfully lighter and smaller, which makes it a very competent solution for people that tends to travel a lot, not to mention that is the cheapest one. Optimate 2 year warranty. I've had 3 (possibly 4) Optimates in 12 years, ... It is for most people- but please, read the Yuasa technical manual. Safety check: OptiMate 4 DUAL PROGRAM will proceed to charge if the battery voltage can maintain above 2V during the initial start up diagnosis, even if the battery was at 0.5V before connection. 3. Functionality: OptiMate 4 DUAL PROGRAM microprocessor checks the system for correct operation (LEDs flash briefly to confirm). I have just purchase an Optimate 4 with the CanBus cable and looking for some advice. My current battery is very weak due to lack of use recently. So I hooked up the Optimate 4 and left on for about 10 hrs day 1 and then about 8 hrs day two.