My Hitachi UC 18YG charger has flashing (not steady) red light when batteries inserted. Both batteries (12 volt EB1215S) no longer charge up to full charge. Is problem with batteries or charger? If charger, is there an easy fix or should I buy new one?

You may want to look for the manual but it is mostly caused by a bad battery. The battery may be discharged far and many chargers are not capable to charge batteries being even close to full. Green means charging and red is fail. It keeps trying. A broken and useless battery may show the same indicators flashing. Inspect the battery to make sure it is in a good condition, like acid at about the right level and no traces of melting on the container or visible loose/bent plates. Put a voltage or multimeter on 20 Volt at its terminals and determine the battery has any voltage to begin with. 11Volt indicates an empty battery and 12,8 to 13,2 is probably full. An empty 12 Volt battery is charged with a 12 Volt ~ 1 Amp power adapter (maximum 1/10 of battery Amp but not until fully charged) and preferably a 1 Amp fuse in the + line. This is "attended charging," meaning things must not get hot and charging is stopped before the battery is full. Then try the charger again, always the 12 Volt clamps attached first and next the plug in the mains. Disconnecting is in reverse order.
Bad batteries often have sulfur on their plates and can be revived by fast discharging but the success rate is low. Meaning a battery can be better but not good enough. Batteries have a life of 5 years and closer to 10 when always charged. When charging was low and often not, the battery could have died after two or three years. This apart from a limited number of charge-discharge cycles. The test is with all lights on and then not dimming in the first minute or after ten seconds. Good batteries must hold charge for a week and not much less every day.

http://www.hitachi-tools.ch/media/wysiwyg/Explosionszeichnungen/UC18YK.pdfhagbye

I live by hitachi, one of the good things about it is lowes will exchange them as long as you have a receipt and it's under 30 days. If not chargers are not very expensive, or you can send it back for repairs. I have 10 of those combo packs and never had a problem with a single one, for you to get 2 is a freak accident.

The Ryobi charger will flash green as it charges and then remain steady or slowly flashing green when fully charged. Flashing red means testing and if it remains steady or slowly flashing red it is defective.

I had the same issue -- charged it for days and still red light flashing. I was ready to break it open and see if I could replace battery. Then I looked on the opposite end of the charger and seen a little round hole thingy. I put the end of a pen in there and pushed it twice and -- the red light went away . Plugged the charge in and steady red then purple and now blue. Looks like that is a reset ..Try it -- it worked for mine.

Charger flashing red indicates the battery is still not full and is in the process of recharging.
Red light steady indicates your battery is fully charged and ready to operate with your Coolpix 5000.
When red light is off it indicates there is no battery inserted or the charger is not pluged in.

If only the red light is flashing then the battery is not charging at all. Ryobi identifies in the manual that batteries will not charge below 43 degress F. If your batteries and charger are in the garage in a cold climate, warm the batteries to room temp in the house and then try again. If the charge starts when the batteries are warm they will continue charging for the full cycle even in a cold area.

I really don't have any idea as to what you're talking about here other than a battery and maybe a charger. Seems as if you're saying that you have a 12 volt 1.5 amp automatic battery charger connected to a 12 volt, 8.5amph battery but the red light on your charger is blinking. The blinking red light indicates that the charger is not seeing a proper connection such as crossed polarity connection or simply a poor connection. You say that the battery voltage has dropped from 12.5 volts to 9.1 volts with the charger connected. If this is the case, the battery is badly discharged and the charger is not charging the battery for some reason. The charger may be bad but check the connections to make certain they are correct and good. If they are, I'd replace the charger.

Good luck
Steve

The control systems on power mobility equipment have a "prevent" circuit that immobilizes the equipment while it is plugged into a charger, so folks won't take off with it plugged into the wall outlet. When you turn it on when plugged into a charger, the display will flash constantly, or sweep constantly, depending on the manufacturer. This is normal. Your off-board charger should have a red light to indicate power to the charger, and another light for the charge status. Yellowish means it is charging, when it turns green, you are fully charged. If the status light is green all the time, that is an indication that the charger is not functioning properly, or that the batteries are below a chargeable state. Check charger output, which should be 26-28 volts dc, and each battery should show at least a 12 volt reading, but around 13.5 volts with a full charge. If one or both of the batteries drops below 12 volts after a short period of time, it's time for a fresh pair. Fully charge new ones before using the chair.