I need a cord and battery charger for model sl21 spotlight

If this is the usual sort of halogen spotlight, it is usually supplied with a mains charger adaptor and a lead to charge it from the car cigar lighter socket.

Both those items are also commonly supplied with a range of car-related rechargeable items, torches, jumpstarters and so forth.
I have several such items and I find the 12 volt lead and mains charging adaptor completely interchangeable between all of them. Rechargeable halogen spotlights generally have a very disappointing battery life of around 20 minutes unless a very expensive professional model is bought.

If it is not a rechargeable type that must be permanently connected to the car cigar lighter, the power cord is usually permanently fixed to the lamp but if it isn't, the cable will need to be substantial enough to carry several amps - something similar to that of perhaps a large coolbox.

6 volts rechargeable battery. Check with the manufacture for a recharger for the 110v and or a car charger for your light.

The short answer is "The tip should be set to positive (+).

I found an old Vector VEC127Y Spotlight. It appeared to be in perfect condition but the battery was dead and there was no charger. I was able to buy a replacement battery at BatteriesPlus for $21 USD. Here is the link for the battery
REPLACEMENT VECTOR VEC127Y BATTERY
I also purchased a Universal A/C adapter to use as a charger at BatteriesPlus for $17 USD. Their site does not list it yet but here is the manufacturers link. Please note the original battery was rated 6Ah. The replacement is only rated for 5Ah. Which means one less Amp hour (Ah). Which means a shorter run time, after charging, than the original battery had. Otherwise they are equal.
UNIVERSAL AC ADAPTER
I installed the new battery. I set the AC Adapter to 6V and installed the largest of the seven adapter tips that came with the charger, with TIP set to be positive (+). I opened the battery compartment of the spotlight and disconnected both the red (positive +) and black (negative -) battery leads from the battery. I then plugged the adapter tip of the Universal AC Adapter into the spotlight and plugged the AC Adapter plug to a power outlet. With a multimeter I tested the polarity of the spotlight battery leads while charging. I was able to confirm that the Adapter TIP should be set to positive (+). After reconnecting the spotlight battery leads and setting the AC Adapter to charge, I have a perfectly great spotlight in full working order.

This model has a built in charger so all you need is an extension cord. You will find the plug in underneath the black rubber flap that is located on the side.

The Vector Spotlight/Inflator has a built in charging system. All that needs to be done to recharge the batteries is to plug an extension cord into it.

Most of the Vector spotlights use a class 2 charger with an output of 12VDC 400ma with a positive (+) center connector, which are very common. I have several of these chargers from different manufacturers, and I use them interchangably on whichever spotlight I happen to plug them into.
One complication with my Vectors is they use a coaxial connector plug on the spotlight end that is a size N, which is being phased out and Radio Shack doesn'd even carry any more. If you hae a box of misc chargers, find a 12VDC one with a connector that fits your 1.5MCP light, and that is probably the one that came with your light.
Note that you can also charge your light with the cigarette lighter adapter cord that came with it. So if you can't find an AC transformer that fits but you have your cigarette lighter adapter cord, you can buy one of those cigarette lighter size gadgets that plugs into an AC outlet, and then plug your cigarette lighter cord into that.

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

While it could be the battery, it could also be the internal charger in the spotlight. When you plug it in, it bypasses the charger and uses the connected power. However, it is likely just a bad battery. The batteries only last 3 years in an ideal setting and since these lights are typically only used certain times of the year, the batteries discharge and go bad. New batteries can be found at: http://batteryinternational.com/spotlight-batteries-vector-battery.html

if its the one im thinking of, i had the same problem.

if you look at the back and theres the male prongs to plug into the wall

well what i did was i took off the back

then i took off the cradle that held the battery in place, and stood it up on the lens and simply plugged it into the wall to charge it.

its kind of complicated but simple way to save some dough in todays market.

6 Volts, here is info from site.
VEC127Y
VECTOR SPORT SPOT 1 MILLION CANDLE POWER CORDLESS-RECHARGEABLE SPOTLIGHT

• HIGH CANDLE POWER QUARTZ HALOGEN BULB DELIVERS A BRIGHT AND TIGHT BEAM
  
• AREA WORKLIGHT IN HANDLE PROVIDES UP TO 15 HOURS OF LIGHT WHEN FULLY CHARGED
  
• PROVIDES CONTINUOUS SPOTLIGHT USE FOR UP TO 25 MINUTES WHEN FULLY CHARGED
  
• HIGH IMPACT, BREAK RESISTANT ABS AND POLYCARBONATE HOUSING
  
• TOUGH, WEATHER RESISTANT AND BUILT FOR RUGGED OUTDOOR USE
  
• REPLACEABLE 6 VOLT, 6 AMP HOUR, NON-SPILLABLE, SEALED BATTERY
  
• LOCKING TRIGGER FOR ON/OFF LIGHT CONTROL
  
• INCLUDES AC AND DC CHARGING ADAPTERS
  
• INCLUDES BUILT IN HANDS FREE WORKSTAND