You could use bicarbonate, but you will need a lot of it, and it will fizz up and make lots of spray. I would suggest using normal sodium carbonate (washing soda). You should be able to buy that cheaply in a big 1 or 2 kg box.
Decant the battery acid into a plastic bucket and then add the soda a little at a time until it stops fizzing. Stir the bucket thoroughly and repeat. Then pour the neutralized mixture down the drain and wash it away with plenty of water. There is nothing hazardous once it is neutralized.
(In fact, "high strength drain cleaner" is concentrated sulphuric acid just like the more dilute acid in batteries, and that gets poured down a drain neat to dissolve blockages. The main reason for neutralizing battery acid is to avoid it corroding metal sinks, grilles or other things.)
Lastly, be very careful not to spill or spash any battery acid on your clothes, and be sure to neutralize and wash away any spills thoroughly. If you get a drop of sulphuric acid on your clothes you are going to find a hole there later on. (Your skin doesn't matter, because once it starts stinging you will know about it.)
Edit: I forgot to mention you should also rinse out the inside of the batteries with water once you have decanted the acid.
Lead salts are extremely toxic and dangerous. You want to filter out the lead before dumping the liquid. It's true that the concentration is small--because it's insoluble--but that also makes it very easy to precipitate and filter.
see:
http://www.sprep.org/solid_waste/documents/Solid%20Waste/Guidelines/Battery%20Management%20.pdf About half way through is a section on Acid Handling.
I'd suggest using sodium carbonate to precipitate the lead, until the pH is between 7-8. Add it very slowly, in small quantities, not chunks, and with short breaks between, not only because of heat, but because it won't precipitate the lead properly if added too fast--keep it cool and you're ok. Then filter it with appropriate chemical-grade filter paper. Toss the neutralized, unleaded liquid down the drain. Take the precipitate and filter paper to a toxic waste facility--just let it evaporate until thoroughly dry and store it away until you have enough to justify a trip. Alternatively, mix it into concrete and toss the whole thing away. The concrete will slow the leeching into the environment. Better to find a toxic dump or recycling facility.
Before you do that, gently rinse the metal pieces with water, add the acid to the rinse water, then proceed to the precipitation. You almost certainly want to dilute the acid before doing this--wasting a gallon of distilled water for the whole procedure isn't a bad idea, especially in hard water areas. Before you're done, rinse the rinse bucket and any containers, including the battery itself, with a little water and precipitate and filter that as well. The leftover in the containers after one or two quick rinses (letting the water run off, not gather inside--use a squeeze bottle, like from a sports drink) is probably small enough for most people's conscience, and if it isn't, just take the battery somewhere unopened.
Keep the place well ventilated, wear gloves & goggles, be near a shower or a lot of water, etc. I haven't done this specifically, so you might want to read that document first.
You do something similar with excess copper (Cu+2) etchant, though you need extra steps to handle the other ions.
For the seriously environmentally conscious... there may be other additives in the acid, in which case we'd be guessing about the safety of what we're pouring down the drain.
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