Well there are a few variables to add to the mix, 1) a Drill has around a 1/4hp on the output side and 2) How old was the drill and what kind of life had it had prior to the test ??,
I have seen Alternators hooked up to all sort of things including pushbikes and stationary motors,
Based on that I can't see it taking around 7hp to power an alternator if someone can get power from one just by peddling a bike, Surely there must be a proper way in order to measure what it takes to drive an Alternator,
I know that wind generator put out very little wattage in relation to their size, but once they get up to about a metre across they start to produce around 500w when max'd out and in a 10mph / 16kph wind they only put out about 10 or 20w and unless the wind is blowing around 30 to 40+kph then most of them struggle just to maintain a bank of batteries just to cover their natural daily loss So if you have 5 X 100Ah batteries loosing 3% a day a wind charger would have to produce 15Ah just to break even and closer to 30Ah just to float them and that is not allowing for the power used in a 24 hour period,
Taking the above in to account depending on the type of batteries being used creates another problem in trying to get the power back in to the batteries, and the cost factor of the type of batteries being used, To stand any change of being able to collect that power AGM would be the bare minimum a person could use, Lead Crystal would be the best option due to the amount of power they can except and being half the price of Lithium.
If the vehicle is not setup to run the 2 later techs then if a person wants the faster charging times then the only way to do that is to run a DC to Dc Charger because the profiles can be set to suit the tech of the battery or by using a Victron MTTP Charge controller and/or Solar, Just because someone hooks up 2 batteries and it runs for a while does not make it the right thing to do, Adding a 100Ah to another 100Ah is just going to make a 200Ah bank and a standard Alternator will never recover those batteries from dead flat not without over heating the alternator at best Or cooking the Alternator at the worst because as the battery size increases so does the Charge time and then the Alternator is having to work Two or Three times as Hard and the Hotter it gets the Less Power it will put out, It's the same as when a power draw Like a Fridge is being run using too thinner power cables where the fridge won't run properly or keeps shutting down, If those 2 Batteries are sucking too much from the Alternator then bad things are going to happen. :/
