Hi Jeff, One of these should do it: http://www1.uk.conrad.com/scripts/wgate/zcop_uk/~flNlc3Npb249UDkwX0NPUF9VSzpDX0FHQVRFMDU6MDAwMC4wMTI2LjlhYjI3ODYzJn5odHRwX2NvbnRlbnRfY2hhcnNldD1pc28tODg1OS0xJn5TdGF0ZT0xMjYxMjE4Nzk3====?~template=PCAT_AREA_S_BROWSE&mfhelp=&p_selected_area=%24ROOT&p_selected_area_fh=&perform_special_action=&glb_user_js=Y&shop=UK&vgl_artikel_in_index=&product_show_id=&p_page_to_display=DirektSearch&~cookies=1&zhmmh_lfo=&zhmmh_area_kz=&s_haupt_kategorie=&p_searchstring=&p_searchstring_artnr=187151&p_search_category=alle&r3_matn=&insert_kz=&area_s_url=&brand=&amount=&new_item_quantity=&area_url=&direkt_aufriss_area=&p_countdown=&p_80=&p_80_category=&p_80_article=&p_next_template_after_login=&mindestbestellwert=&login=&password=&bpemail=&bpid=&url=&show_wk=&use_search=1&p_back_template=&template=&kat_save=&updatestr=&vgl_artikel_in_vgl=&titel=&darsteller=®isseur=&anbieter=&genre=&fsk=&jahr=&jahr2=&dvd_error=X&dvd_empty_error=X&dvd_year_error=&call_dvd=&kna_news=&p_status_scenario=&documentselector=&aktiv=&p_load_area=$ROOT&p_artikelbilder_mode=&p_sortopt=&page=&p_catalog_max_results=10
I would go for a Li-Po since they are light weight and small for a handheld device like this. Perhaps it is a good idea to use a replacement battery for a cell phone, they are nice and compact. The one I have got in my cell is 6 x 39 x 65 mm 3.6Volts and 1200mAh 26g as an example. ;)
Not enough info, what is it? What voltage? What is the expected use and run time? How much current does it require, is it constant or erratic? Used inside or outside, in winter?
There is a perfectly logical explanation for this: Volvo is since a few yers completely owned by Ford! ;D BTW, for the topic; Bob Blick has something to add about oxygen sensors here: http://www.bobblick.com/techref/projects/o2sensor/o2sensor.html
If you take out the regulator there will be other problems since the voltage over the transistor will be much higher (more heat)! Can you measure the voltage over the LED/resistor while fully lit? It would be very helpful to know some data for your LED
I thought maybe you had already decided on a specific type of relay suitable for audio. I am not sure if there are some special requirements for such relays?