Replacing battery in backup sump pump

I'm going to second mikes advice about wearing rubber gloves and safety glasses, especially if you can't guarantee that the container is properly sealed. If you get any on you, simply flush with lots of water, and apply a paste of baking soda and water to neutralize (I would flush first while someone else mixes the paste). For transport, just make sure that you have something that will keep it from tipping over.

OK, now to the reason I answered: places that you can take it.

The easiest is if your town or city sponsors a hazardous waste day or provides a hazardous waste dropoff (more likely in a large city). Call first to ensure that they take acids. Most will, especially acids that are commonly used in home improvement, such as sulfuric and hydrochloric (aka muriatic).

If you have a relationship with a repair shop, you can call and see if they'll take it (for use with batteries). They probably won't, and a stranger definitely won't, but it's worth asking.

A metal plating shop is another possibility. They probably won't accept it for use, but might dump it into their waste drum for a nominal charge.

Finally, if mikes scared you, there's Clean Harbors or similar companies. They'll come to your house and scare you even more, and you'll pay through the nose. But it will be gone.

I was headed this way until about 2009. In the most modern and expensive setups you might have all the devices communicating and coordinating. In most, each one has its charging parameters that it's trying to meet, and the only communication is the voltage on the bank.

With multiple, uncoordinated charge controllers you may exceed the optimum charging current, and you should expect to have disagreements among uncoordinated charge controllers (and a water turbine with no charge controller) as their charging set-points and algorithms are almost certainly different.

If you have the money to put into it, or you see it as saving money on the battery bank's lifetime, a set of networked, coordinated smart charge controllers would certainly work more optimally (and can all work at the same time) - but you should also realize that any system that won't leave you in the dark for large parts of the year is going to have some excess capacity when everything is going well, charging-wise.

You can't simply add more battery without making it really hard to get it fully charged and equalized, and you can't reduce power sources without finding yourself in the dark after a few dry, cloudy, windless days. So sometimes, you are going to be dumping excess power. If you can do something useful with that power, great; (laundry is a good one, often) otherwise it's just part of the cost of having power more of the time. In the case of a fuel burning generator and a wind turbine, common sense would be to shut down the fuel-burner on a windy day.