A Sky D100 LiPo charger can be used to Fast Charge, Slow Charge, Storage Charge, Balance Charge and Discharge as well as Resistance Check LiPo batteries.
Other types of battery can also be charged, but I am only mentioning the LiPo functions here as it is the type that is currently the most used in r/c model boats.
The charge speed can also be adjusted as can the highest voltage point to determine the charging cut-off point etc..
Two batteries can be attached individually to Channel A or Channel B and each battery can have a different function or be of a different type or voltage etc..
The Storage Charge will take each battery to it's ideal storage voltage and with the cells balanced .
The parameter's can also be adjusted as required too, so it saves the need to buy a lot of separate units and cab switch function at the touch of a button
All in one place and very good at what it does really well - and can Independently charge two at a time (or one).
They come with a pair of balance boards and a selection of charge leads as well as a good instruction book.
These can be bought new or used - I bought my last one used from eBay at a very good price!
Also available as an Overlander RC-D100 and well worth looking out for.
Bob.