Hi just my opinion here but may help someone,
For the cost of around £25-£35 I fit an Acumate (there are others on the market) battery charger to my bikes. Just 2 simple connections to the battery into one lead that can be poked in a crevase under the seat but allows me to charge the battery without taking battery out or removing anything just attach it to the charger and charge it up every now n then seems to do the trick and have fitted them to all my bikes..Also as a rule when I buy a bike (second hand projects usually) I usually invest in a new battery as not sure of the condition or how long the one with bike has been left at least then I know the batterys age and its started in good condition...
Anyone agree/disagree or got any other useful products/advice