Found a display model Norelco 7000 is it functional like the regular ones you buy

Replacements for model 7310XL can be found at shaveroutlet.com
Norelco Philips HQ8 Spectra Sensotec Precision Replacement Heads

Model 8894XL uses one battery and it can be found at shaveroutlet.com here:
http://shaveroutlet.com/norelco-philips-liion-battery-cell-for-select-models-p-510.html

Yes, they are replaceable. You didn't mention your model number but batteries can be found at shaveroutlet.com.

See video below fro basic replacement instruction
http://www.youtube.com/watch?v=2oAnLpvdYqQ

Did you use part HQ9 for your replacements? Norelco makes many different replacement heads and only one type is correct. The correct type for model 8140XL can be found at shaveroutlet.com below

http://shaveroutlet.com/norelco-philips-hq9-replacement-heads-p-252.html

Correct batteries for your model can be found at shaveroutlet.com. See link bewlow

http://shaveroutlet.com/shaver-replacement-parts/batteries/philips-norelco/shaver-battery-pack-for-most-norelco-more-p-278.html

Videos for disassembly and installation can be found at links below

http://www.youtube.com/watch?v=rGD84BfKxAE

http://www.youtube.com/watch?v=2oAnLpvdYqQ

Power cord for model 5801XL can be found at shaveroutlet.com
Universal Shaver Cord Coiled for Most Models

You will find batteries for model 6705X at shaveroutlet.com. See link below

http://shaveroutlet.com/shaver-replacement-parts/shaver-battery-pack-for-most-norelco-more-p-278.html

Scroll down item page for viedo tutorials for installation tips

norelco 580xl replacement heads

philips norelco hq56 replacement heads for electric shaver philips norelco 5801xl blades. More detail at http://www.menelectricrazor.com/norelco-5801xl-replacement-heads/

Norelco 5810xl replacement heads is Norelco HQ56 reflex plus replacement heads.

Here's a source for the replacement heads and cutter blades for your Norelco 7737. If you need any other parts, they also have them available.

http://www.electricshaverstore.com/get_item_hq177_norelco-cool-skin-7000-series-head-set.htm

Hope you find this Very Helpful and best regards!