Think I'll plonk this in here. Might be handy for someone. 
Rate of battery charging.----The main thing is to keep the battery temperature low. ( Around bath water temperature. ) Much hotter than this and the water content will start to get boiled off.
In the days when batteries had filler caps you could look inside to see what was happening. 20 amps for any length of time and you'd see fierce action as bubbles came up past the plates.
The regulator is there to stop this happening. Fast chargers that are some times used by garages can drastically shorten the life of batteries. ( Avoid fast chargers like the plague. )
With the latest modern batteries the fluid levels drop but can no longer be checked. Also paste can be forced out of the lead/antimony grids and fall to the bottom of the battery.
None of this does the battery any good.
RE---- Charging rates and capacity.
A batteries voltage does not change much from full to empty. Somewhere around one volt is normal unless the battery has been subjected to deep discharge.
Capacity however goes through an enormous change.
The analogy of two water tanks describes it perfectly.
Two tanks 3 feet high.
Tank 1 being a foot diameter.
Tank 2 being 10 feet diameter.
With reference to a battery the pressure in both is identical. ( Read DEPTH as VOLTAGE. )
The volume/ capacity in tank 2 is vastly greater than in tank 1 even though the depth/ voltage is identical.
Connect the tanks together and there is no flow from one to the other.
Raise the level in either tank and water will start to transfer from the higher to the lower. ( battery 12 volts---Charger 14 volts. Current starts to flow. Battery charges. )
Batteries------Around 12 volts discharged. Apply a higher voltage such as the alternator supplies ( !4.4 volts approx ) and current starts to flow into the battery increasing its capacity. ( Amount of electricity stored within it and available for work. ) During this time the battery internal voltage slowly increases and the current flow slowly decreases. The battery temperature starts to drop.
14.4 volts translates into around 5 amps roughly.
Any voltage increase above this will increase the current supply in proportion.
The higher the voltage the hotter the battery will get. ( As said above, avoid garage fast chargers like the plague. )
A discharged Diesel engine battery will take around 30 hours on a standard charger.
Colvert.
( Refer to post 73 too for a bit more info. Lol. )