Do I likely have a bad battery or altenator?

For the first time and out of the blue yesterday my 2000 ford ranger had problems starting up. It started though then randomly died while I was at a gas station and I had to have it jumped, it took a long time for it to start with the jump. Once started I took it straight home and parked it since it has so much trouble starting. This morning I went to see if it starts and it started right up without a problem. What's with the inconsistency?

Could be a battery issue

Battery the altenator could also be failing to keep it charged.

My guess is it is the alternator. Depending on the vehicle, the alternator can have the regulator go bad and most of those are replaceable. Disconnect the battery, remove the alternator and take it to a shop to have it tested. Some shops specialize in starter and alternator testing, rebuilding and repairs. It depends on how big a town you live in. I had a battery die on me once in my Ford service truck. I was able to get jumped off, but it would not stay running unless we disconnected the battery. I immediately drove to a parts store and got a new battery and never had another problem. Most places, like Advance Auto, will test your battery for free.

Lets separate the two with easy tests.

#1. Take your battery to any store that sells new ones other than Auto Zone. Ask for a free 15 second battery *load test which will tell you the reserve amperage capacity. Amperage spins starter motors not voltage.

#2. When a new or fully charged battery has been installed, touch the battery terminals with an inexpensive volt meter *set at 20 volts with the engine running. IF the alternator is charging properly the volt meter will read between 13.5 - 14.2 volts.

Its ez start your car unhook battery ground if car keeps running your alternator is good if it dies your alternator is bad take battery and have it "load" tested a machine is needed auto zone is free