25++ vs 55++ battery

Without any further info it is likely related to the battery capacity. The 25++ is probably the standard battery that comes with the laptop. The 55++ is an optional upgrade for a larger battery with longer battery life which means the laptop will be a little more bulkier and heavier.
 
Quite an interesting question - I had to find out, it is a measurement I had never seen in batteries and I use a lot of exotic batteries in my other hobbies.
The number system 25+, 25++, 27++, 55+, & 55++ used by Lenovo have to do with Watt/Hours for the respective battery with higher number having more watt/hours and therefore more life under a given load.
Very different if you ask me.
 

longth

Commendable
Sep 1, 2016
1
0
1,510
+ means 6 Cell and ++ means 9Cell
The number before the 'plus' symbol is the version of the battery correspond to the laptop series. For example, my laptop genre is Thinkpad W520 and it can use 55 or 70 battery. You can search for your battery versions which are best suite to your laptop on shoplenovo. Good luck!