1985 Corvette. Voltmeter is reading low, 11.1. What may be causing this? Time for a new battery?

Check for a blockage in the exhaust system, if OK check ignition timing as low grade fuel can be a cause.

see howmuch the alternator charge.
take voltmeter ,run the engine and see the reading on the voltmeter.it chould be somewhere 14.50 volts on the batterie.
if you read 12 or 13 volts is too low

start the car. if you have a volt meter at the battery you should have 13 to 14 volts while running. if not your alternator isnt working.

Most systems work like this, in any vehicle. You have a switch to turn it on. You have a relay that is energized by the switch. The relay supplies power to the windshield wiper motor when energized. So to troubleshoot you check to see if there is power in the motor terminals . No power there, check the relay to see if it has been energized. If there is power to the relay, no power to the motor, you have a bad relay. If the relay is not receiving power to the coil, then check your switch. You need a voltmeter, Radio Shack has them for very little money.
Hope that helps.
Joe.

Stop by any good parts store and have your charging system tested. Most will do it free. Or if you have a voltmeter, attach to battery while idling and reading should be 13.1v-14.8v - anything less you need an alternator.

One of two issues may be at hand...
You have a slow draw, as in a glove box door light staying on, or something like that...
or...your battery is failing. You can get that tested at auto parts stores, better if removed.

You didn't mention how far if any you drove since installing battery. First jump start, put voltmeter in battery while idling - should read 13.1v-15.8v. Anything less, replace alternator. If good, load test new battery.

16.9 v will blow every bulb in the vehicle and damage any sensitive electronics. You alternator is runing wide open.and not charging. Actually its the regulator in the altrnator. It will cook your battery as well. need replace and battert check. - good luck

Battery probably getting weak. A load test will tell you for sure, and most parts places will do that for free, especially if your buying a new one if required. Even when a battery reads 12 volts, once load on it, if it drops too low, it's time for a new one.

In my 1985 corvette the battery is located under the hood, but you must remove the panel on the driver's side to gain access to the battery. Hope this helps