What does it mean when the recharge (red) light is blinking while mouse is on charger? The model number isNWOM5.

Red flashing means it is a non-rechargeable or incompatible battery. The charger is meant for NiMH batteries.
http://www.panasonicbatteryproducts.com/eneloop_rechargeable_batteries/advanced-individual-quick-ni-mh-battery-charger

Try a friend's good Eneloop battery. If that flashes red, then the charger probably has a manufacturing defect.

Here's a guide;
What do the battery lights mean on my mouse? Some keyboard and mouse models feature a battery light that shows the current status of the batteries. The following table describes the different lights and states.
Light
Device Model Status Single long green blink Rechargeable Batteries are good. This occurs when batteries are first installed or every time that the device is turned on. Slow green blink Rechargeable Device is docked in the charging station and is charging properly. Steady green Rechargeable Device is docked in the charging station and does not need additional charging. Steady green Presenter Mouse (Japanese version) Laser pointer is on. Red/green blink Wireless Device is discoverable (trying to connect to the transceiver). Slow red blink Non-rechargeable Batteries are low and need to be replaced. Slow red blink Rechargeable Batteries are low and need recharging. Fast red blink Rechargeable Device is docked in the charging station, but there is a charging error.
Reasons for errors: The wrong type of battery is installed; the battery or batteries are missing; or the battery connection is bad.
Solutions: Make sure that the correct battery or batteries are installed, and are installed correctly. If necessary, remove the batteries, wipe them with a clean cloth, and reinsert them. Steady red Presenter Mouse (Standard version) Laser pointer is on.

It's indeed the low batteries indicator. I have a Lenovo N30 myself.
I suggest you use a good pair of rechargeable AAA batteries.
They last longer than regular alkaline.
Best regards.
Source: Lenovo N30 User's Manual. Own experience.

When the green light stays on that means the battery is fully charged. The correct charger for that light is a Class 2 Transformer
Model: KA12D120030042U It has a output of 12VDC at 300 mA

Try a new or other charger, problem may be with the charger.

if the battery is very flat, the red light blinks.
try sliding the little battery switch off for a few seconds, then on again, and have the charger connected

the steady red light showing when in charger shows that
it is charging. the blinking red light when taken out of
charger or turned on and off means it is not fully charged.
leave it in charger till red light turns green.

I had the same problem with the mouse MX1000 not charging when it is on its charger.
Then, I realized that I forgot to plug the adapter for the charger - this charger is not taking its power from the USB port but from an external charger!
Once I plugged the charger, the mouse recharged without any problem.
I hope this helps.
This mouse is really great, once this question of recharge is solved.
Stephan

I found the following:

Red light slow blinking: Battery Low, please put mouse in charger and charge;

When in Charger Red light Slow Blinking: No charging, please check and clean Gold Plated contacts in charger and Mouse;

When in Charger green light Blinking: Charging in progress

When in Charger green light Steady: Charging complete

When in Charger Red light Fast Blinking: Mouse detects overvoltage during charging! Please clean Battery contact inside Mouse, or replace rechargable batteries NiMh 1500-2100 mAh only