93 XJ Sport 4L HO Check Engine Light & Low Voltage question

9 times out of 10 when I start my Jeep the check engine light comes on and shows 9 - 10 volts. Does anyone have any information that may be helpful to correct this. This is our only vehicle and only mode of transportation. It's been a good Jeep and has never let me down. It has about 218,000 miles on it. Thanks for any help! :gonnablow

First thing I would do would be to clean all the battery connections and verify all the grounds such as the one on the firewall and the rear head bolt near the firewall are clean and have good tight connections.

Do you have access to a Volt Ohm meter so you can check voltages at the battery at rest and check the alternator output voltage with engine running?
Need to do some testing to see whats going on....
Battery at rest should be 12.5 to 13.0 volts DC. When the vehicle is running with headlights, A/C, etc.... OFF; the voltage should be 13.3 to 14.5 volts DC.