91 b2200 alternator?

went out about a month ago. Replaced with cheap duralast and worked fine... except the check engine and battery light came on right after install, but only when going 55mph or faster.
Last week, new one went out and replaced it again with identical duralast.
Now, check engine and battery light stay on all the time.
Battery is only about a year old.

What do you think I should look at first to figure out what the problem is?

91 b2200 4 cyl. Manual. Carb.
(Also, when distributor cap came loose a few weeks ago, I discovered that the distributor came out of an 87 model because the cap and rotor a got for a 91 wouldn't fit at all.(freakin Craigslist..))

You might look at the battery ground cable for internal corrosion or where it grounds to the block for corrosion there. If you have a meter, you can check for running voltage at the battery. It should be between 13.8 and 14.6 volts DC. If a cable goes bad it causes the alternator to work harder trying to charge the battery and that could be where your issue is coming from.

I'll have to ask my old man if he's got a device to check running voltage and I'll check out the cable. Thanks and I'll let you know what I find out.
Is it possible, since the guy I got it from seems to have Frankensteined it a bit with parts from different years that I might need a different year model?
I'm obviously not a mechanic, but all the alternator does is charge the battery, correct? Could it be possible I have the wrong battery as well or would that be obvious?

Thanks again

"You might look at the battery ground cable for internal corrosion or where it grounds to the block for corrosion there. If you have a meter, you can check for running voltage at the battery. It should be between 13.8 and 14.6 volts DC. If a cable goes bad it causes the alternator to work harder trying to charge the battery and that could be where your issue is coming from. "

Do that test. A digital multimeter with 0 - 20 volts DC scale is under $25 to free at Harbor Freight with a coupon.

Measure that voltage across the battery terminals with engine running; do NOT remove a battery cable while the engine is running (you have an alternator, not a generator). Autozone and O'Reilly can check that for charging if you drive there, and free.

Yes, the alternator keeps the battery at charge so it can spin the engine to start it, and to keep it at that state. Yes, a bad battery can affect things.

My '88 B2200 with 215K still has its original alternator; but I replaced the alternator in my '98 Frontier with a rebuilt (lifetime) one from O'Reilly about 5 years ago, and it has held up fine.