This may be from age, on all parts in the system. Although a tough call. Lots of times the problem is in the wiring - as in, loose or corroded wiring.
Might need to take a day and take apart the battery connections - all of them from the post to junction block at the battery onto the cables from that junction block. It's the batteries breakout box for heavy current and power routing.
If you can't seem to fix it - at least you solved one major problem from reoccurring again once connections are redone and made solid so current can flow again. There's other areas too...
It may be that corrosion and the Oxides From March (read: Seasonal changes from winter to spring and water - moisture entry) have gained a foothold and are eating up any exposed metal - like copper - with acids from the battery posts leaking out onto them.
Other signs are loose or worn bearings in the alternator causing charging issues from belt slippage from seized bearings or belt slip - or even corroded terminals from seals breaking down due to age and heat. Might need to have your charging system inspected or even tested. Alternators can set you back about $150 + USD even rebuilt aren't cheap.
Added:
- OK, so why no Battery Light on the Dash?
Because the Alternator "Sense" wire that goes back to the PCM is connected and is communicating to the Powertrain Control Module and it's telling the rest of the system that it is producing output. Even a secondary effect of the main power cable from the Battery Junction Box, is kept in Range by the PCM and the Alternator - thru it's own connection to the Mains back at the batteries junction block. This keeps the light off, but does not help the system do or perform a health check on the battery.
- It's not readily programmed to diagnose the problem with poor battery power connections - except when the Alternator itself is failing - and that is when the PCM can not communicate to the Alternator to make it produce power or change the power produced by the Alternator as a diagnostic - it will set the Dash light for this condition.
- However this setup is not able to diagnose a bad battery or a bad connection from the terminals of the battery to the rest of the cars electrical system.
-- In Some Titanium Models (Read upper Trim classes) there is a Battery Monitor system that when it sees a battery voltage level drop below a threshold, it cuts out the ground side of the Battery by disconnecting - Electrically Isolating the Battery from - the Ground cable to prevent the complete drain of the battery when the engine is not running. It's not foolproof, and it will only work if it's installed correctly - for numerous charging fails and engagement of the Monitor to keep the battery from being drained and destroying itself - it will set NOT ONLY the Alternator Light (Battery SYMBOL) but a Pile Symbol Light (Schematic symbol of a battery - for its PATS Alarm systems are also affected), the Check Engine light and even to force it into a LIMP MODE to make you take it to the shop.
- Vehicle's Engine Bay shown above is for an SE which does not have oi use a Battery Monitor - it would be a module on the Ground side cable at the rear of the battery.
